Conventionally, as disclosed in Patent Literature 1, for the purpose of enhancing fuel efficiency or the like, an engine including a plurality of cylinders performs switching between a reduced-cylinder operation in which a part of the cylinders is deactivated by stopping opening and closing operations of the intake valves and the exhaust valves of the part of the cylinders, and by stopping combustion in the part of cylinders; and an all-cylinder operation in which opening and closing operations of the intake valves and the exhaust valves of all the cylinders are enabled, and combustion is performed in all the cylinders.
In an engine configured to perform switching between a reduced-cylinder operation and an all-cylinder operation, at the time of switching from one of the reduced-cylinder operation and the all-cylinder operation to the other thereof, a valve to be opened first, or a valve to be closed first is determined, out of the intake valves and the exhaust valves of a deactivated cylinder. For instance, there is a case, in which an intake valve of a deactivated cylinder is started to open first for the purpose of speedily activating the deactivated cylinder at the time of switching from a reduced-cylinder operation to an all-cylinder operation. Further, there is a case, in which an exhaust valve of a deactivated cylinder is started to open first for the purpose of confirming the opening and closing states of the exhaust valve of the deactivated cylinder. Further, there is a case, in which an exhaust valve of a deactivated cylinder is started to close first for the purpose of causing combustion gas to remain in the deactivated cylinder at the time of switching from an all-cylinder operation to a reduced-cylinder operation.